Generally, substrates to be typically used, such as semiconductor substrates exemplarily made of silicon, gallium arsenide (GaAs), gallium nitride (GaN) and the like, and a glass substrate for display, are two-dimensional planar substrates, respectively.
The semiconductor substrates such as made of silicon, GaAs, and the like are each provided and used in a manner to pull up a molten raw material by using a seed crystal to thereby fabricate an ingot of single crystal, and to cut it into semiconductor substrates, followed by application of grinding and polishing to provide them with mirror surfaces, respectively.
In case of a liquid-crystal oriented TFT (thin film transistor) comprising semiconductor thin films formed on a two-dimensional glass substrate, a polycrystalline silicon (hereinafter abbreviated to “p-Si”) or an amorphous silicon (hereinafter abbreviated to “a-Si”) is deposited on a multicomponent two-dimensional (planar) glass substrate by a vacuum process such as a plasma CVD (hereinafter abbreviated to “PCVD”). In case of p-Si, it is achieved to grow a crystal grain into a larger grain diameter, so as to improve a performance of a TFT. In this case, the p-Si is locally heated by laser, in a manner to melt and solidify the p-Si by moving the laser, thereby growing the crystal in a direction of a horizontal plane of a substrate (this is called “lateral crystal growth”). This forms a p-Si recrystallizedly grown in a line along which the laser was moved. It is required to repeat this procedure until achievement of a predetermined width.
Note that upsized two-dimensional substrates have been developed up to now, so as to decrease a fabricating cost of two-dimensional substrates. Upsized substrates are developed to have a size of 730×920 mm in the fourth generation in the year 2002, and a size of 1,100×1,300 mm in the fifth generation in 2003, and it is thus predicted that the sixth generation in 2004 to 2005 will have a size of 1,500×1,800 mm.
Substrates to be each used for a liquid crystal display or a solar cell are provided and used by grinding and polishing a plate glass such as prepared by a float process, and by cutting it into a predetermined size. Depending on the usage, such glass is possibly used by cutting only, without grinding and polishing.
Meanwhile, concerning a display, there has been filed by SARNOFF CORPORATION located in the United States a Japanese patent application 2000-601699 (P2000-601699) disclosing an invention configured to integrate light emitting devices into a fiber which is rectangle, circular or the like in cross section, and to integrated fibers are brought them into an array to establish a planar display.
In case of adopting a conventional two-dimensional substrate, upsizing a display increases the number of pixels proportionally to the square of a screen size. As a result, upsizing a screen considerably deteriorates a yield, when a defect occurrence ratio is unchanged. This naturally leads to an increased fabricating cost per one display, thereby problematically and considerably increasing a fabricating cost in inverse proportion to the yield. This is because, when even one portion of a screen has a defective device, it is impossible to replace only the portion or an area around it so as to repair the screen.
According to the invention by the SARNOFF CORPORATION, it is possible to replace only a fiber including a defective device integrated therewith to thereby repair the screen, thereby providing an advantage of a remarkably improved yield. Also disclosed in this patent-related reference, is a fabricating method of a fiber including devices integrated therewith.
According to the method adopting a fiber substrate (linear substrate) disclosed in the patent-related reference, it becomes possible to downsize a producing apparatus of a display as compared with a conventional method for adopting a two-dimensional substrate. Further, the disclosed method is advantageous in equipment investment and production yield, since a size of each surface to be worked can be downsized by achieving a width of a linear substrate which is commensurate with a width of each device, thereby allowing a fine working with a higher precision.
In the method of the patent-related reference, since it is required to fabricate a large number of linear substrates, various processes related to the production of linear substrates are to be excellent in productivity. In this patent-related reference, it is explained in the patent-related reference that a columnar magnetron plasma source is used to enable CVD and sputtering deposition at higher rates, respectively. Further, it is to be achieved to provide a plurality of chambers between a fiber supply reel and a winding reel, thereby continuously or intermittently conducting treatments for cleaning, and for depositing a transparent electrode (ITO, SnO2, ZnO, or the like), electric conductor (Cu, Al, or the like), OLED (organic EL), electrodes (Mg/Ag, Ca/Al, or the like), and protective film (oxide film, nitride film, or the like).
Since the transparent electrode (ITO, SnO2, ZnO, or the like) and electric conductor (Cu, Al, or the like) are continuously deposited on each linear substrate in the longitudinal direction thereof, it becomes possible to adopt a pre-worked linear substrate which results in a treatment process excluding the corresponding procedures. As a fabricating method of the pre-worked fiber, it is disclosed to obtain the same by coating an ITO layer, electric conductor, or another desired layer onto a quartz fiber just after drawing it.
There will be now explained a related art of a solar cell. Solar cells are each capable of directly converting a substantially exhaustless solar energy into an electrical energy, thereby serving as a clean energy. Based thereon, solar cells each acts as one of the energies, which never cause environmental problems, and to which an attention is directed as an alternative of thermal power generation using a fossil fuel. Only, due to an increased fabricating cost of solar cells, it is a present state in Japan that an electricity rate based on power generation by solar cells is about 70 yen/kWh (2003) which is about three times as expensive as an electricity rate of 25 yen/kWh of the mains-power.
Presently, there are mainly utilized solar cells each adopting a single crystal silicon substrate or polycrystalline silicon substrate which is excellent in conversion efficiency. In this case, it is typical to adopt a P type substrate, and to dope phosphorus (P) into a surface of the substrate to thereby bring the surface into an N type semiconductor, thereby forming a PN junction in a thickness direction of the substrate. Further, the substrate is formed with electrodes at an obverse surface and a reverse surface of the substrate, respectively, and the surfaces of the substrate is coated by a protective film(s) of silicon dioxide (SiO2) or silicon nitride (Si3N4), thereby establishing a solar cell. Further, there is provided a solar cell module by integrating a plurality of the solar cells into a panel, and there is further provided a solar cell array by integrating a plurality of the modules. This solar cell array is combined with a discharge/charge controller, battery, inverter, or the like, thereby establishing a solar cell system.
Meanwhile, there has been disclosed a technique concerning a solar cell without using silicon substrates. This is to use a multicomponent glass substrate (blue plate glass or white plate glass) as a substrate. The glass substrate is formed thereon with a film of SiO2 at a relatively low temperature of about 300° C. by sputtering, vapor deposition, CVD or the like, and there is further formed thereon a transparent electroconductive film of ITO (InSnO2), SnO2, ZnO, or the like by sputtering. Further deposited on the transparent electroconductive film is amorphous silicon (hereinafter abbreviated to “a-Si”) by a PCVD method. Devices are each provided in a structure of PIN diode comprising three layers of P type, I type, and N type, for example. Further deposited on the a-Si is a reverse surface electrode by vapor deposition, sputtering, or the like. Since the a-Si can be deposited at a low temperature, it is possible to form it into a transparent film. In the solar cell as described above, there is used a substrate having a size of 1 m2 and a thickness of 4 mm. As a result, its weight becomes as heavy as about 9 kg.
In addition to the above description, there have been also investigated binary compound semiconductors such as GaAs, InP, CdS, CdTe or the like, or ternary compound semiconductors such as CuInSe2. Further, there has been also developed a pigment-impregnated solar cell comprising a porous TiO2 impregnated with pigment. There has been further developed a solar cell utilizing organic semiconductor. Also in these solar cells, semiconductor substrates or glass substrates are used.
Further, described in U.S. Pat. No. 5,437,736 (Semiconductor Fiber Solar Cells and Modules) is an invention configured to provide solar cells each obtained by coating an electroconductive layer such as molybdenum (Mo) onto a curved face of an optical fiber and by partially forming first and second semiconductor layers in arched shapes on the optical fiber, so as to array the solar cells in a planar shape to thereby form a solar cell module. In the described invention, it is shown to deposit Mo by a fiber-drawing process in FIGS. 14, 17 of the U.S. Patent. Deposited on the fiber wound on a spool are two semiconductor films in a separate process, followed by deposition of a transparent electrode, thereby establishing a solar cell.    Patent-related reference 1: Japanese Patent Application No. 2000-601699    Patent-related reference 2: U.S. Pat. No. 5,437,736